پاورپوینت کامل Chapter 10: XML 66 اسلاید در PowerPoint

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پاورپوینت کامل Chapter 10: XML 66 اسلاید در PowerPoint

اسلاید ۴: XML Introduction (Cont.)The ability to specify new tags, and to create nested tag structures make XML a great way to exchange data, not just documents.Much of the use of XML has been in data exchange applications, not as a replacement for HTMLTags make data (relatively) self-documenting E.g. <bank> <account> <account_number> A-101 </account_number> <branch_name> Downtown </branch_name> <balance> 500 </balance> </account> <depositor> <account_number> A-101 </account_number> <customer_name> Johnson </customer_name> </depositor> </bank>

اسلاید ۵: XML: MotivationData interchange is critical in today’s networked worldExamples:Banking: funds transferOrder processing (especially inter-company orders)Scientific dataChemistry: ChemML, …Genetics: BSML (Bio-Sequence Markup Language), …Paper flow of information between organizations is being replaced by electronic flow of informationEach application area has its own set of standards for representing informationXML has become the basis for all new generation data interchange formats

اسلاید ۶: XML Motivation (Cont.)Earlier generation formats were based on plain text with line headers indicating the meaning of fieldsSimilar in concept to email headersDoes not allow for nested structures, no standard “type” languageTied too closely to low level document structure (lines, spaces, etc)Each XML based standard defines what are valid elements, using XML type specification languages to specify the syntaxDTD (Document Type Descriptors)XML SchemaPlus textual descriptions of the semanticsXML allows new tags to be defined as requiredHowever, this may be constrained by DTDsA wide variety of tools is available for parsing, browsing and querying XML documents/data

اسلاید ۷: Comparison with Relational DataInefficient: tags, which in effect represent schema information, are repeatedBetter than relational tuples as a data-exchange formatUnlike relational tuples, XML data is self-documenting due to presence of tagsNon-rigid format: tags can be addedAllows nested structuresWide acceptance, not only in database systems, but also in browsers, tools, and applications

اسلاید ۸: Structure of XML DataTag: label for a section of dataElement: section of data beginning with <tagname> and ending with matching </tagname>Elements must be properly nestedProper nesting <account> … <balance> …. </balance> </account> Improper nesting <account> … <balance> …. </account> </balance> Formally: every start tag must have a unique matching end tag, that is in the context of the same parent element.Every document must have a single top-level element

اسلاید ۹: Example of Nested Elements <bank-1> <customer> <customer_name> Hayes </customer_name> <customer_street> Main </customer_street> <customer_city> Harrison </customer_city> <account> <account_number> A-102 </account_number> <branch_name> Perryridge </branch_name> <balance> 400 </balance> </account> <account> … </account> </customer> . . </bank-1>

اسلاید ۱۰: Motivation for NestingNesting of data is useful in data transferExample: elements representing customer_id, customer_name, and address nested within an order elementNesting is not supported, or discouraged, in relational databasesWith multiple orders, customer name and address are stored redundantlynormalization replaces nested structures in each order by foreign key into table storing customer name and address informationNesting is supported in object-relational databasesBut nesting is appropriate when transferring dataExternal application does not have direct access to data referenced by a foreign key

اسلاید ۱۱: Structure of XML Data (Cont.)Mixture of text with sub-elements is legal in XML. Example: <account> This account is seldom used any more. <account_number> A-102</account_number> <branch_name> Perryridge</branch_name> <balance>400 </balance> </account>Useful for document markup, but discouraged for data representation

اسلاید ۱۲: AttributesElements can have attributes <account acct-type = “checking” > <account_number> A-102 </account_number> <branch_name> Perryridge </branch_name> <balance> 400 </balance> </account>Attributes are specified by name=value pairs inside the starting tag of an elementAn element may have several attributes, but each attribute name can only occur once<account acct-type = “checking” monthly-fee=“۵”>

اسلاید ۱۳: Attributes vs. SubelementsDistinction between subelement and attributeIn the context of documents, attributes are part of markup, while subelement contents are part of the basic document contentsIn the context of data representation, the difference is unclear and may be confusingSame information can be represented in two ways<account account_number = “A-101”> …. </account><account> <account_number>A-101</account_number> … </account>Suggestion: use attributes for identifiers of elements, and use subelements for contents

اسلاید ۱۴: NamespacesXML data has to be exchanged between organizationsSame tag name may have different meaning in different organizations, causing confusion on exchanged documentsSpecifying a unique string as an element name avoids confusionBetter solution: use unique-name:element-nameAvoid using long unique names all over document by using XML Namespaces <bank Xmlns:FB=‘http://; … <FB:branch> <FB:branchname>Downtown</FB:branchname> <FB:branchcity> Brooklyn </FB:branchcity> </FB:branch> …</bank>

اسلاید ۱۵: More on XML SyntaxElements without subelements or text content can be abbreviated by ending the start tag with a /> and deleting the end tag<account number=“A-101” branch=“Perryridge” balance=“۲۰۰ />To store string data that may contain tags, without the tags being interpreted as subelements, use CDATA as below<![CDATA[<account> … </account>]]>Here, <account> and </account> are treated as just stringsCDATA stands for “character data”

اسلاید ۱۶: XML Document SchemaDatabase schemas constrain what information can be stored, and the data types of stored valuesXML documents are not required to have an associated schemaHowever, schemas are very important for XML data exchangeOtherwise, a site cannot automatically interpret data received from another siteTwo mechanisms for specifying XML schemaDocument Type Definition (DTD)Widely usedXML Schema Newer, increasing use

اسلاید ۱۷: Document Type Definition (DTD)The type of an XML document can be specified using a DTDDTD constraints structure of XML dataWhat elements can occurWhat attributes can/must an element haveWhat subelements can/must occur inside each element, and how many times.DTD does not constrain data typesAll values represented as strings in XMLDTD syntax<!ELEMENT element (subelements-specification) ><!ATTLIST element (attributes) >

اسلاید ۱۸: Element Specification in DTDSubelements can be specified asnames of elements, or#PCDATA (parsed character data), i.e., character stringsEMPTY (no subelements) or ANY (anything can be a subelement)Example<! ELEMENT depositor (customer_name account_number)> <! ELEMENT customer_name (#PCDATA)><! ELEMENT account_number (#PCDATA)>Subelement specification may have regular expressions <!ELEMENT bank ( ( account | customer | depositor)+)>Notation: “|” – alternatives “+” – ۱ or more occurrences “*” – ۰ or more occurrences

اسلاید ۱۹: Bank DTD<!DOCTYPE bank [<!ELEMENT bank ( ( account | customer | depositor)+)><!ELEMENT account (account_number branch_name balance)><! ELEMENT customer(customer_name customer_street customer_city)><! ELEMENT depositor (customer_name account_number)><! ELEMENT account_number (#PCDATA)><! ELEMENT branch_name (#PCDATA)><! ELEMENT balance(#PCDATA)><! ELEMENT customer_name(#PCDATA)><! ELEMENT customer_street(#PCDATA)><! ELEMENT customer_city(#PCDATA)>]>

اسلاید ۲۰: Attribute Specification in DTDAttribute specification : for each attribute NameType of attribute CDATAID (identifier) or IDREF (ID reference) or IDREFS (multiple IDREFs) more on this later Whether mandatory (#REQUIRED)has a default value (value), or neither (#IMPLIED)Examples<!ATTLIST account acct-type CDATA “checking”><!ATTLIST customercustomer_id ID # REQUIREDaccounts IDREFS # REQUIRED >

اسلاید ۲۱: IDs and IDREFsAn element can have at most one attribute of type IDThe ID attribute value of each element in an XML document must be distinctThus the ID attribute value is an object identifierAn attribute of type IDREF must contain the ID value of an element in the same documentAn attribute of type IDREFS contains a set of (0 or more) ID values. Each ID value must contain the ID value of an element in the same document

اسلاید ۲۲: Bank DTD with AttributesBank DTD with ID and IDREF attribute types. <!DOCTYPE bank-2[ <!ELEMENT account (branch, balance)> <!ATTLIST account account_number ID # REQUIRED owners IDREFS # REQUIRED> <!ELEMENT customer(customer_name, customer_street, customer_city)> <!ATTLIST customer customer_id ID # REQUIRED accounts IDREFS # REQUIRED> … declarations for branch, balance, customer_name, customer_street and customer_city ]>

اسلاید ۲۳: XML data with ID and IDREF attributes<bank-2><account account_number=“A-401” owners=“C100 C102”> <branch_name> Downtown </branch_name> <balance> 500 </balance></account><customer customer_id=“C100” accounts=“A-401”> <customer_name>Joe </customer_name> <customer_street> Monroe </customer_street&gt